Slow leakers are a persistent problem in lamp manufacture. A slow leaker allows oxygen to seep into the enclosed lamp cavity to destroy the seals or filaments. The lamp then fails. A typical leaker has a life that is about 4% of the lamp's rated life. Some lamps are commonly enclosed in an outer jacket to protect the light generating capsule. The outer jacket may act as a simple shield, or may include a reflector, and lens structure to direct the light generated by the inner capsule. In either case, the enclosed volume is filled with a non-oxygen gas to protect the inner capsule. Nonetheless, oxygen may still enter the enclosed volume, either due to a mistake in the original filling and sealing, or because of leaks in the outer envelope.
For high output lamps, for example studio lamps, costly capsules, reflectors, coatings, lens, and bases are all brought together in one expensive product. If the lamp leaks and fails prematurely, the customer is naturally unhappy. There is then a need for identifying lamps that may be leakers before they are shipped to customers.
Zirconium, and other metal combinations are known to getter evaporating or outgasing materials that may cloud the lamp, or may interfere with the lamp chemistry. Getters are designed to control the materials, and the by products of the original lamp manufacture. Getters are not usually designed to absorb the gases infiltrating through leaks, nor are getters usually designed to accommodate improperly filled lamps. In either case, a common getter has only a small capacity for absorbing stray materials, and would likely be overwhelmed by improper fills, and leaked gases. Also, while a getter may be effective at trapping an improper material, getters usually operate over an extended period of time, and not within the short testing period available in an assembly line. There is then a need to rapidly indicate an improper fill or leak in a sealed lamp. Examples of the prior art are shown in U.S. Pat. Nos. 2,203,896, 2,203,897, 3,626,229, 3,805,105, 3,926,832, 4,200,460, 4,624,520.
U.S. Pat. No. 2,203,896 issued to Jan H. de Boer shows an incandescent lamp with two zirconium getters. One getter is designed to absorb hydrogen products, and the other is designed to absorb oxygen.
U.S. Pat. No. 2,203,897 issued to Antonius de Graaff shows an incandescent lamp bulb enclosing a gas fill including nitrogen. A zirconium getter is used, but limited for operation from 200.degree. C. to 600.degree. C. The zirconium then acts as a getter for hydrogen and hydrogen products.
U.S. Pat. No. 3,626,229 issued to Henry S. Spacil shows an arc discharge capsule positioned in an outer envelope. A zirconium getter is placed in the enclosed volume as a hydrogen getter.
U.S. Pat. No. 3,805,105 issued to Warren C. Gungle shows an arc discharge capsule positioned in an outer envelope. A zirconium getter is placed in the enclosed volume as a hydrogen getter. The getter is specially positioned to maintain its temperature of operation.
U.S. Pat. No. 3,926,832 issued to Aldo Barosi shows a gettering structure composed of metal powders, including zirconium. The porosity of the metal structure enhances the getter.
U.S. Pat. No. 4,200,460 issued to Leonard N. Grossman shows a getter composed of zirconium, nickel and titanium. The getter is able to absorb water, carbon dioxide, oxygen and others gases.
U.S. Pat. No. 4,127,790 issued to Gijsbert Kuus shows an arc discharge lamp with a getter including zirconium among other metals.
U.S. Pat. No. 4,624,520 issued to Anton J. Bouman shows an arc discharge lamp with a zirconium interrupt switch positioned between the inner capsule and outer envelope. If the outer capsule is broken, the zirconium switch oxidizes, causing the switch to open and extinguish the lamp.